Freshwater Pea Clam (Pisidium volutabundum)

Sketch of P. volutabundum from Vanatta 1910

Shells in the genus Pisidium are very small freshwater clams known as pea clams, pill clams or fingernail clams. Psidium volutabundum is a species which is endemic to Bermuda. It was first described by E.G. Vanatta in 1910 from specimens collected at Pembroke Marsh. He describes the shell as follows: “Shell equivalve, suborbicular, umbones moderately prominent, thin, horn colour, superior margin nearly straight, anterior margin subtruncate, inferior margin arcuate, posterior margin convex. Surface finely striate with irregular lines of growth. Hinge arcuate, narrow, ligament scar concave with a slight longitudinal ridge in the centre. The right valve with one large cardinal and two laterals at each end, the lower ones the largest. The left valve provided with two cardinals the lower recurved and a little anterior, a very heavy lateral at each end of the hinge line, with a deep groove between it and the edge of the shell. Alt. 2.56, diam. 1.73, length 3.13 mm.” This little clam is listed as Critically Endangered under the Protected Species Act.